Oxidative cleavage of S‐Arylmercaptoacetic acids by pyridinium chlorochromate: Kinetic and correlation analysis

Kinetics of oxidation of 24 S‐Arylmercaptoacetic acids (SAMA) by pyridinium chlorochromate (PCC) have been studied in acidmedium. The product of oxidation is the corresponding thiophenol. The rate data of meta‐ and para‐substituted acids have been correlated well with σ_I, σ_R^o values and the meta‐compounds correlate well with F,R values. The reaction constants are negative and of smaller magnitudes. Further, the ortho‐substituted acids show a good correlation with triparametric equation involving Taft's σ_I and σ_R^o and charton's steric parameter v. There is no considerable steric contribution to the total orthosubstituent effect. Based on these observations, the mechanism involving the formation of protonated arylsulfinylacetic acid intermediate, followed by an intramolecular rearrangement leading to the product thiophenol has been proposed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 683–688, 1999     

Quantitative determination of sodium perborate and sodium percarbonate in detergent powders by infrared spectrometry

Sodium perborate (SPB) and sodium percarbonate (SPC) are solid compounds which act as sources of H₂O₂ in solution for stain bleaching, being considered as oxidizing agents in washing powder. This research deals with the quantitative determination of SPB and SPC by an analytical procedure based on attenuated total reflectance Fourier transform infrared spectrometry, utilizing partial least squares for data processing in the 1600-800 cm⁻¹ spectral region. The statistical parameters such as R ², standard error of prediction and relative standard deviation have been evaluated, while number of factors, number of scans and resolution were optimized. The standard deviation of method was 0.006 and 0.010 for SPC and SPB, respectively.     

Oxidative C-C bond cleavage of N-alkoxycarbonylated cyclic amines by sodium nitrite in trifluoroacetic acid

Oxidative carbon-carbon bond cleavage of N-alkoxycarbonylated cyclic amines was accomplished by NaNO₂ in TFA to afford ω-amino carboxylic acid in high yield. Optically active 3-hydroxypiperidine derivatives and 3-pipecolinate were converted to enantiomerically pure (R)-4-amino-3-hydroxybutanoic acid (GABOB) and (S)-2-pyrrolidone-4-carboxylate, respectively.     

Oxidative heck-type reaction involving cleavage of a carbon-phosphorus bond of arylphosphonic acids

Cleavage of a carbon-phosphorus bond is achieved under palladium catalysis in an oxidative Heck-type reaction which exploits arylphosphonic acids. The reaction of arylphosphonic acids with alkenes provides arylation products in good yields in the presence of TBAF with trimethylamine oxide as an oxidant.     

四正丁基过硫酸铵氧化裂解2，4-二硝基苯腙衍生物的反应研究

四正丁基过硫酸铵在1,2二氯乙烷溶剂中可高产率地使醛和酮的2,4-二硝基苯腙衍生物氧化裂解成相应的羰基化合物,其分子中碳碳双键,氰基,酯基和缩醛基等基团均不受影响。同时探讨了可能的反应机理和反应溶剂对氧化裂解反应的影响。     

A comparative study on chemical treatment of jute fiber: potassium dichromate, potassium permanganate and sodium perborate trihydrate

Studies have been carried out on chemical treatments of jute fibers in order to hinder moisture absorption, which causes incompatibility with a non-polar polymer, and to increase the surface roughness for mechanical interlocking. The objective of this research is to improve the interfacial adhesion between jute fibers and polypropylene by oxidative treatments. On this basis, jute fibers were treated with potassium dichromate (PD), potassium permanganate (PM) and sodium perborate trihydrate (SP). Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy were used to characterize jute fibers. The effects of chemical treatments were also revealed by assessment of moisture absorbability, yarn tensile properties and interfacial shear strength with polypropylene. FTIR and XPS analyses confirmed oxidative modification of jute fibers using any of the surface treatments. It was observed that the proportion of O=C groups increased, whereas that of O–H groups decreased after oxidative modifications. Tensile strength and elasticity modulus results decreased after oxidative treatments, whereas PD, PM and SP enhanced the interfacial shear strength values by 25, 61 and 71 %, respectively. Only SP treatment influenced moisture absorbability results significantly. The surface roughness of untreated jute fibers shows increments after chemical treatments due to partial removal of surface cementings. According to the findings obtained from surface characterization methods and physical tests, the highest interfacial adhesion with better compatibility with polypropylene was achieved after SP treatment by providing the highest surface roughness values and hydrophobic character of jute fiber.     

Kinetics and mechanism of oxidation of bromide ions by sodium perborate by transforming to a Landolt process

Sodium perborate was used for oxidation of bromide ions at pH 3.64. The reaction was conducted by potentiometric measurements. The orders with respect to perborate and bromide ions were found to be unity in each reagent and a plausible mechanism was postulated. The effect of temperature was studied in the range of 20–40 °C and the Arrhenius parameters were evaluated.

---

pH=3,64. . , . 20–40 °C, .

     

Oxidative cleavage of cellulose by fungal copper-dependent polysaccharide monooxygenases

Fungal-derived, copper-dependent polysaccharide monooxygenases (PMOs), formerly known as GH61 proteins, have recently been shown to catalyze the O(2)-dependent oxidative cleavage of recalcitrant polysaccharides. Different PMOs isolated from Neurospora crassa were found to generate oxidized cellodextrins modified at the reducing or nonreducing ends upon incubation with cellulose and cellobiose dehydrogenase. Here we show that the nonreducing end product formed by an N. crassa PMO is a 4-ketoaldose. Together with isotope labeling experiments, further support is provided for a mechanism involving oxygen insertion and subsequent elimination to break glycosidic bonds in crystalline cellulose.     

Oxidative Dissolution of Silver Nanoparticles by Dioxygen: A Kinetic and Mechanistic Study

We have recently reported a kinetic and mechanistic study on oxidative dissolution of silver nanoparticles (AgNPs) by H₂O₂. In the present study, the parameters that govern the dissolution of AgNPs by O₂ were revealed by using UV/Vis spectrophotometry. Under the same reaction conditions (Tris‐HOAc, pH 8.5, I=0.1 M at 25 °C) the apparent dissolution rate (k_app) of AgNPs (10±2.8 nm) by O₂ is about 100‐fold slower than that of H₂O₂. The reaction rate is first‐order with respect to [Ag⁰], [O₂], and [Tris]_T, and inverse first‐order with respect to [Ag⁺] (where [Ag⁰]=total concentration of Ag metal and [Tris]_T=total concentration of Tris). The rate constant is dependent on the size of AgNPs. No free superoxide (O₂⁻) and hydroxyl radical (⋅OH) were detected by trapping experiments. On the basis of kinetic and trapping experiments, an amine‐activated pathway for the oxidation of AgNPs by O₂ is proposed.     

Photosensitized DNA cleavage promoted by amino acids

A novel class of DNA cleavage agents are reported that derive activity from amino acids tethered to a photoactive intercalator.     

Selective cleavage of ethers by sodium iodide-acyl chloride

Cyclic and acyclic ethers are regioselectively cleaved at less substituted α-carbon-oxygen bond in the absence of Lewis acid by the reagent system of sodium iodide and acyl chlorides.     

Kinetics and mechanism of the catalysed decomposition of sodium perborate by the ethylenediaminetetraacetatoiron(III) complex

The rate of reaction of [Fe^IIIY] (Y = EDTA anion) with NaBO₃ was studied in aqueous 0.1 M NaNO₃ at various temperatures. The observed rate constant,k _obs = kKKK ₁[FeEDTA(H₂O)^-]/{[H⁺] + KK ₁[FeEDTA(H₂O)^-]}applies over the pH range studied. The monohydroxy complex, [FeEDTA (OH)]^2– is the catalyst which reacts with the peroxy ion to produce a violet intermediate complex. The composition of perborate confirms to Michaelis–Menten kinetics, the rate-determining step involving breakdown of the intermediate complex. The activation enthalpy and activation entropy were calculated.     

Oxidative cleavage of ribofuranose 5-(α-hydroxyphosphonates): a route to erythrofuranose-based nucleoside phosphonic acids

We report here an oxidative cleavage of (5R)- and (5S)-ribofuranosyl-5-C-phosphonate derivatives with periodate anion under both strong acidic and neutral conditions. In both cases, only (5R)-configured compound underwent the expected oxidation reaction and afforded the desired (4R)-erythrofuranosylphosphonate, whereas the second epimer, (5S)-ribofuranosyl-5-C-phosphonate did not provide the corresponding (4S)-erythrofuranosylphosphonate derivative. This different behavior of epimers toward oxidative cleavage is an important phenomenon. The obtained (4R)-erythrofuranosylphosphonate was used for the preparation of phosphonate mimic of adenosine 5′-phosphate via classical nucleosidation reaction. Condensation of the protected shortened AMP analogue with adenosine derivatives, however, provided only the 2′,5′-linked ApA analogue. Study on hybridization of the modified 2′-5′ ApA with polyU revealed its ability to form stable triplex-like complex, similar to natural 2′-5′ r(ApA) and 3′-5′ r(ApA). NMR spectroscopy study showed that the erythrofuranose part of the phosphonate nucleotide unit of modified 2′-5′ ApA was predominantly in the C2′-endo conformation, which is characteristic for B-DNA.     

Oxidative cleavage of 1-alkylcyclopentanols by lead tetraacetate-metal chloride system

Conclusions Oxoalkyl radicals are generated when the lead tetraacetate-alkali or alkaline earth metal chloride system is reacted with 1-alkylcyclopentanols, which are oxidized to chloroketones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2383–2385, October, 1979.